Internal heater for rf apertures

ABSTRACT

A heater for a radio frequency (RF) antenna and method for using the same are disclosed. In one embodiment, an antenna comprises a physical antenna aperture having an array of RF antenna elements; and a plurality of heating elements, each heating element being between pairs of RF elements of the array of RF elements.

PRIORITY

The present patent application claims priority to and incorporates byreference the corresponding provisional patent application Ser. No.62/364,722, titled, “Internal Heater for RF Apertures,” filed on Jul.20, 2016.

FIELD OF THE INVENTION

Embodiments of the present invention relate to the field of radiofrequency (RF) apertures used for communication; more particularly,embodiments of the present invention relate to RF apertures, such as,for example, antennas, that include internal heaters.

BACKGROUND

Certain antenna technologies require heating of the antenna in order tobring the antenna to an operational temperature. For example, certainantennas that utilize liquid crystals must have the liquid crystalsheated to a specific temperature in order for the liquid crystal tooperate as desired.

In prior art related to liquid crystal displays (LCD), resistive heatingelements are used to keep the LC above a specific temperature for properoperation, for example in automotive display applications where ambienttemperatures can reach −30 C to −40 C. These heating elements are madefrom transparent conductors, such as Indium Tin Oxide (ITO) on aseparate glass substrate from the primary LCD substrate. This substrateis subsequently bonded to the primary LCD substrate to provide thermalconductivity. Because the heating element is transparent to opticalfrequencies, this is a straightforward and practical way to implement aheater for LCDs, even though the heating element is in the signal path.

This approach, however, is not feasible when considering LC-basedantennas. Because ITO and similar materials are not transparent at RFfrequencies, placing these types of heater elements in the path of theRF signal will attenuate the RF signal and degrade the performance ofthe antenna.

Consequently, prior art embodiments of LC-based antennas use resistiveheating elements attached to the metal feed structure or other bulkmechanical structures with good thermal properties to heat an internalportion of the antenna where the LC layer resides. However, because theresistive heating elements are physically separated from the LC layer bya number of layers in the antenna stack-up, including layers of thermalinsulators, significantly more heat power must be applied in order toheat the liquid crystal, as compared to the LCD implementation.

Other implementations of LC-based antenna heaters attempt to heat the LClayer from the edges of the antenna aperture. These embodiments require400-500 W of power and require 30-40 minutes at this power to bring theLC layer to operational temperatures. This is an inefficient use ofheating power resources.

SUMMARY OF THE INVENTION

A heater for a radio frequency (RF) antenna and method for using thesame are disclosed. In one embodiment, an antenna comprises a physicalantenna aperture having an array of RF antenna elements; and a pluralityof heating elements, each heating element being between pairs of RFelements of the array of RF elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1A illustrates heating wires with equal line lengths following gateand heater routing between RF elements.

FIG. 1B illustrates heating wires with unequal lengths on concentricarcs between RF elements.

FIGS. 2A-2C illustrate an example cross section of one embodiment of anantenna aperture.

FIG. 3A illustrates an example of a heater bus placement for heaterwires of equal length.

FIG. 3B illustrates an example of heater bus placement for heater wiresof unequal length.

FIG. 4A illustrates an example of heater buses crossing a border sealbetween layers in an antenna aperture.

FIG. 4B illustrates a generic cross section of a heater bus connectingto a heater wire inside an antenna aperture, extending under a seal andcoming out to the bond pad structure on an iris layer overhang.

FIG. 5 illustrates a heater bus electrical crossover from an iris layerto a patch layer inside a border seal.

FIG. 6 illustrates a heater bus electrical cross over from an iris layerto a patch layer within a border seal structure.

FIGS. 7A-7C illustrate typical thin-film transistor (TFT) current(I)-voltage (V) curve at various temperatures.

FIG. 8A is a flow diagram of one embodiment of a process for determiningan estimate of temperature of the LC using a TFT (or other type oftransistor).

FIG. 8B is a circuit arrangement for measuring voltage and current foruse in determining temperature within an antenna aperture.

FIG. 8C is a flow diagram of one embodiment of a process for determiningan estimate of temperature of the LC using a TFT (or other type oftransistor).

FIG. 8D is another circuit arrangement for measuring voltage and currentfor use in determining temperature within an antenna aperture.

FIG. 9 illustrates an arrangement for measuring capacitance of liquidcrystal.

FIG. 10 illustrates an aperture having one or more arrays of antennaelements placed in concentric rings around an input feed of thecylindrically fed antenna.

FIG. 11 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.

FIG. 12 illustrates one embodiment of a tunable resonator/slot.

FIG. 13 illustrates a cross section view of one embodiment of a physicalantenna aperture.

FIGS. 14A-D illustrate one embodiment of the different layers forcreating the slotted array.

FIG. 15 illustrates a side view of one embodiment of a cylindrically fedantenna structure.

FIG. 16 illustrates another embodiment of the antenna system with anoutgoing wave.

FIG. 17 illustrates one embodiment of the placement of matrix drivecircuitry with respect to antenna elements.

FIG. 18 illustrates one embodiment of a TFT package.

FIG. 19 is a block diagram of an embodiment of a communication systemhaving simultaneous transmit and receive paths.

FIG. 20 is a block diagram of another embodiment of a communicationsystem having simultaneous transmit and receive paths.

FIG. 21 illustrates one embodiment of a superstrate having heatingelements for heating inside an antenna aperture.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following description, numerous details are set forth to providea more thorough explanation of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Embodiments of the invention include techniques for placing heaters(e.g., heating elements) on the interior of the liquid crystal cell ofLC-based, radio frequency (RF) antenna apertures. In one embodiment, theheaters are placed inside the antenna aperture near the RF elements andcloser to liquid crystal (LC) that is part of the RF antenna elements.This allows for more direct heating of the aperture, lessens the heaterpower requirements, and shortens the temperature rise time overtechniques that use more indirect heating methods of raising thetemperature inside the aperture, e.g., resistive heating elements on theback of the feed structure.

It is important that the heater implementation not interfere with the RFproperties of the aperture. In one embodiment, the heater elements(e.g., heater traces) are located within the antenna aperture atlocations that reduce, and potentially eliminate, RF interference whileproviding more direct heating within the aperture. In one embodiment,this is accomplished by putting heating elements between the RF elementson nearly the same plane as the RF elements. In one embodiment, thelocation of the heater elements is in the same plane as the iriselements of an iris layer that is part of a patch/iris slotted-arrayantenna. By moving the heater wiring inside the aperture onto nearly thesame plane as the iris metal, the interaction of the heating wires withthe RF signal is reduced, and potentially minimized.

The techniques disclosed herein also include methods for detecting thetemperature within an antenna aperture. In one embodiment, thetemperature is detected from a transistor directly on a transistorbackplane. In one embodiment, the transistor backplane is a thin-filmtransistor (TFT) backplane. In one embodiment, if the transistors on thetransistor backplane are in contact with an LC or other material,detecting the temperature of a transistor provides an indication of thetemperature of the LC/material.

Techniques described herein decrease the cost of the heater system,require less power, decrease the rise time of the aperture temperature,and shrink the footprint of the controller board used to control theantenna. More specifically, in one embodiment, techniques describedherein require 75-100 watts of power and will bring the LC layertemperature to operational temperature in 20 minutes.

Furthermore, temperature is typically sensed on the break-out printedcircuit board (PCB), which is substantially physically removed from theglass assembly that includes patch and iris glass layers and an LClayer. On-glass temperature sensing provide much tighter control of thethermal management feedback loop.

Overview

In one embodiment, the heater structure consists of several parts: theheating elements, heater power buses to supply the heater elements, andconnection schemes to connect the heater power buses to the heater powersupplies that are located outside the aperture. In one embodiment, theheater elements are wires. In one embodiment, the heater power buses areof very low resistance.

The implementation of heater wiring, heater buses, and heaterconnections, depending upon implementation, may require additionaldepositions of conductor layers, passivation layers, via openings and soon during aperture fabrication. These additional layers may serve tobuild the heater structures, isolate the heater structure electricallyor chemically from other structures, and to provide interfaces for theheater to existing aperture structure as needed.

Heating Wires

It is desirable that the heating of the aperture occur uniformly. Twoconfigurations of heating wires are described herein that may achievethis objective.

In one embodiment, the heating wires are of equal length and the crosssections of these heating wires are the same (or similar) in dimensionover the length of the heating wires and from heating wire to heatingwire. In the aggregate, this provides the same power dissipation perunit area over the aperture. In one embodiment, the heating wires areevenly distributed over the aperture quality area, with heating wireslaying between irises, not crossing or contacting the patches or irises.In one embodiment, the heating wires are close to the same distanceapart from each other (the same pitch) across the aperture area.

FIG. 1A illustrates an example of heating elements used to heat the RFantenna elements in an antenna aperture, where the heating wires haveequal line lengths and follow gate routing and heater routing between RFelements. In one embodiment, the gate routing is the routing to controlgates that turn on and off liquid crystal-based RF antenna elements,which is described in more detail below.

Referring to FIG. 1A, an antenna aperture segment 100 illustrates onequarter of an antenna array of RF antenna elements. In one embodiment,four antenna aperture segments are coupled together to form an entirearray. Note that other numbers of segments may be used to construct anentire antenna array. For example, in one embodiment, the segments areshaped such three segments coupled together form a circular array of RFantenna elements. For more information on the antenna segments and themanner in which they are coupled together, see U.S. Application PatentPublication No. US2016/0261042, entitled “ANTENNA ELEMENT PLACEMENT FORA CYLINDRICAL FEED ANTENNA”, filed on Mar. 3, 2016 and see U.S.Application Patent Publication No. US2016/0261043, entitled “APERTURESEGMENTATION OF A CYLINDRICAL FEED ANTENNA”, filed on Mar. 3, 2016. Notethat the techniques described herein are not limited to operate withantenna aperture segments and may be used on single apertures thatcontain an entire array of RF antenna elements.

Heating wires (elements) 101 are shown on antenna aperture segment 100.In one embodiment, the heating wires 101 are equal in length. In oneembodiment, heating wires 101 are located between RF antenna elements(not shown) in the antenna array. In one embodiment, heating wires 101follow the gate lines used to control gates to turn on and offindividual RF antenna elements in the array. In one embodiment, heatingwires 101 are equal distance between the RF elements.

In one embodiment, heating wires 101 are equal distance with respect toeach other. In other words, the separation between pairs of heatingwires is equal. Note that this is not a requirement, though it may helpwith providing more uniform heating of the antenna aperture. In oneembodiment, when the antenna elements in the antenna array are locatedin rings, individual heating wires in heating wires 101 are equaldistance between two consecutive rings of RF antenna elements. Inalternative embodiments, the separation between pairs of heating wiresis not equal.

It should be noted that the heater wiring depicted in FIG. 1A indicatesthe relative position and routing of the wiring, but does not representthe wiring size or number of wires. For example, in one embodiment,every other wire may be removed with the remaining wires providing thenecessary heating where the heating is provided uniformly over an area.With respect to the size of the heating wires, their size is based onthe material properties of the heating wire itself and the amount ofheating the wires are to provide.

In one embodiment, the heating wire cross section (height and width) ofheating wires 101 is chosen in the following way. First, the requiredpower for heating the aperture area is converted, for a given desiredheater supply voltage with the number and length of the heating wires,to a resistance for the heating wires. In turn, this resistance value isused in conjunction with properties of the heating wire materials todetermine the required heating wire cross section. Note that otherconsiderations may be used to select the heating wire cross section,including, but not limited to fabrication yields.

In another embodiment, the heating wires are unequal in length and theircross sections are not equal. In one embodiment, where the heating wireswith unequal lengths are on concentric arcs between RF elements. In oneembodiment, the heater wire widths are equal and the wire heights areadjusted radially from the center of the segment to provide uniformpower per unit area over the aperture area.

FIG. 1B illustrates an embodiment of the heating wire on an antennaaperture having heating wires of unequal length and their cross sectionsare unequal to each other. Referring to FIG. 1B, heating wires 111 areshown on antenna aperture segment 110, which is the same type ofaperture segment as depicted in FIG. 1A. In one embodiment, a number ofantenna apertures are coupled together to form a complete antenna array.As in FIG. 1A, in one embodiment, the heating wires are routed betweenthe RF elements. In one embodiment, that routing follows the gaterouting for the gates that control the antenna elements.

In one embodiment, an objective is still to provide nearly uniform powerdissipation per unit area. In this case, however, the height of theheating wire cross sections are varied over the aperture area to controlthe current and resistance to provide the same power dissipation perarea although the heating wires are of unequal length.

It should be noted that the heater wiring depicted in FIG. 1B indicatesthe relative position and routing of the wiring, but does not representthe wiring size or number of wires. With respect to the size of theheating wires, their size is based on the material properties of theheating wire itself and the amount of heating the wires are to provide.

In one embodiment, the heating wires lie between the iris features anddo not cross or contact the patch or iris features in a tunable slottedarray of antenna elements having patch/slot pairs. In the illustrationexamples provided in FIGS. 2A-2C, the heating wires lie in rings midwaybetween the rings of iris/patch elements, with an additional inside andoutside ring of heating wires. In one embodiment, the rings of heatingwiring are on concentric rings at the same radial pitch over theaperture area. In one embodiment, the heater wiring radial pitch is thesame radial pitch as the RF elements. In alternative embodiments, theheater wiring radial pitch is not the same as the radial pitch of the RFelements.

In one embodiment, the heater wires lie close to equidistant between theRF elements.

FIGS. 2A-2C illustrate an example cross section, or side view, of anantenna aperture having iris and patch layers. Referring to FIGS. 2A-2C,patch layer 201 and iris layer 202 are separated with respect to eachother include patch and iris slots, respectively, to form a tunableslotted array. Such an array is well-known and is also described in moredetail below. In one embodiment, patch layer 201 and iris layer 202 areglass substrates. Note that the patch layer and iris layer may bereferred to below as a patch glass layer and an iris glass layer,respectively. However, it should be understood that for purposes herein,the embodiments that include “patch glass layer” and “iris glass layer”may be implemented with a “patch substrate layer” and an “iris substratelayer,” respectively, (or patch substrate and iris substrate) when thesubstrate is other than glass.

Patch metal 211 is fabricated onto patch glass layer 201. A passivationpatch layer 231 is fabricated over patch metal layer 211. A liquidcrystal (LC) alignment layer 213 is fabricated on top of passivationpatch layer 231. Sections of iris metal layer 212 are fabricated ontoiris glass layer 202. Passivation iris layer 232 is fabricated over theiris metal 212. Heating wire 240 is fabricated on top of passivationiris layer 232. In one embodiment, heating wire 240 is close to equaldistance between a pair of iris elements. Other heating wires are alsolocated between iris elements in this fashion. Another passivation layer233 is fabricated over passivation layer 232 and heating wire 240. LCalignment layer 213 is fabricated on top of passivation iris layer 233.

Note that the LC alignment layer 213 is used to align the LC 260 so thatit is pointing in a single direction in a manner well known in the art.

Heater Power Buses

Power buses are provided to supply power to the heating wires. Examplesof these are illustrated in the figures below. In one embodiment, thepower buses are of low resistance when compared to the heater wires, byseveral orders of magnitude, so that there is a small voltage drop fromone end of the bus to the other, so that all of the heating wires mayhave the same voltage at each bus end of the heating wire. This makes itsimpler to manage the power distribution to the network of heatingwires.

In one embodiment, the heater buses are placed inside the aperture sothat the heating wires are able to connect to the proper supply voltagesat each end of the heating wire.

In one embodiment, the heater buses are separate structures placed intothe apertures solely for the purpose of providing power to the heaterwire network.

In another embodiment, existing structures in the aperture may be usedto also act as heater buses. In one embodiment, the heater bus (orbuses) are built into the seal structure of the aperture. In anothercase, the iris metal (e.g., copper) plane may be used as a heater bus tosink or source current for the heating wires.

FIG. 3A illustrates an example of heater power bus placement integratedon an antenna aperture for heater wires of equal length. Referring FIG.3A, antenna aperture segment 300, which represents one of the antennasegments that are coupled together to form an entire antenna array,includes heater bus lines 301 and 302. Heater power bus lines 301 and302 are electrically connected to and provide power to heating wires303.

FIG. 3B illustrates an example of heater power bus placement integratedon an antenna aperture for heater wires of unequal length. Referring toFIG. 3B, heater power buses 303 and 304 are electrically connected toheating wires 305 on antenna aperture segment 310.

Heater Bus to Power Supply Connection

In one embodiment, heater buses on the inside of the aperture arebrought outside of the aperture structure to make connection to theheater power supply. In one embodiment, this can be accomplished byconnecting the heater buses through a border seal structure at the outerportion of the antenna aperture to a metallization layer on one of thelayers in the aperture outside the aperture border seal. For example,one such metallization layer is on the iris glass layer or on the patchglass layer. This metallization connects to the heater buses inside theseal and extends from inside the seal, through the seal, and out toportions of the patch or iris glass layers that extend beyond eachother. These may be referred to as overhang regions. In such cases,portions of the patch or iris glass layers beneath those overhangregions may be referred to as under-hang regions.

FIGS. 4A and 4B illustrate examples of the heater buses coming throughthe border seal out onto the iris glass layer overhang. In oneembodiment, the RF aperture, in this case, is cut so that both the irisglass layer and the patch glass layer have overhang regions (where thesubstrate has a metallized region not faced by glass layer opposite themetallized face). Note that while the iris and patch layers may bedescribed herein at times as glass layers, they are not limited to beingglass and may constitute other types of substrates.

FIG. 4A illustrates a heater bus connection scheme for use in connectingthe heater bus to a heater power supply. Referring to FIG. 4A, in oneembodiment, the heater power supply (not shown) is located outside ofthe antenna element array, such as antenna element array 430, whichincludes the heating wires. Antenna aperture segment 400 includes apatched layer and an iris layer as discussed herein. A portion of theiris layer, referred to as iris overhang 401 and 402 extends overportions of the patch layer. Similarly, a portion of the patch glasslayer, referred to herein as the patch overhang 403, extends beyond apart of the iris glass layer. The iris glass layer and the patch glasslayer are sealed together with an aperture border seal 460. Heater powerbus 410 crosses border seal 460 at seal crossing 421. Heater bus 411crosses border seal 460 at seal crossing 420 and connects to a powersupply. In both cases, heater power bus 410 and heater bus 411 are ableto connect through a power supply by exiting antenna aperture segment400. Antenna aperture segment 400 includes heater power buses 410 and411 electrically connected to heating wires 481 in the antenna elementarray 430.

FIG. 4B is a generic cross section of a heater bus connecting to aheater wire inside the aperture, extending under the seal and coming outto the bond pad structure on the iris overhang. Referring to FIG. 4B,heater bus metal 443 goes under a border seal, border seal adhesive 450,on the iris glass layer 431 on top of passivation layer 446. Thus,heater bus layer 443 is underneath border seal adhesive 450. Border sealadhesive 450 couples the patch layer 430 to iris glass layer 431including the fabricated layers thereon.

Heating wire 444 is deposited on top of passivation layer 446 and aportion of heater bus metal 443, thereby electrically connecting topower bus metal 443 with heater wire 444. Heater wire 444 is fabricatedon a portion of passivation layer 441 that is fabricated on top of irismetal 445 and is fabricated onto a portion of heater bus metal 443. Inan alternative embodiment, there is a passivation layer between heaterbus metal 443 and heating wire 444 with a via through the passivationlayer connecting heater bus metal 443 and heating wire 444.

Passivation layer 441 is fabricated on top of heating wire 444 and atleast a portion of heater power bus metal 443. An alignment layer 432 isfabricated on top of passivation layer 441. Passivation layer 441 isalso fabricated on the bottom of the patch layer 430. Similarly,alignment layer 432 is fabricated over a portion of passivation layer441 on the patch layer 430. Note that while heater wire 444 is showndeposited directly on top of heater bus metal 443 without a passivationlayer and via in between, in an alternative embodiment, another layer ofpassivation is deposited between heater wire 444 and heater bus metal443 with an electrical connection between the two being made using avia. This layer of passivation protects the heater bus metal while theheater wire metal is being etched.

Bond pad/connector structure 442 is a location to electrically connectthe power supply to heater bus metal 443.

The power for the heater buses may cross from the patch glass layer sideof the aperture to the iris glass layer side of the aperture inside ofthe border seal, within the border seal itself, or outside of the borderseal. Bringing the heater buses out to the patch layer overhang has theadvantage of possibly making the heater connection within the connectorused for the rest of the interface lines from the controller electronicsto the aperture. The following illustrations show methods of doing thisinside and within the border seal.

FIG. 5 illustrates on embodiment of a heater power bus electricallycrossing over from iris layer to the patch layer inside a border seal.Referring to FIG. 5, patch glass layer 501 is shown over iris glasslayer 502. There are a number of layers fabricated onto patch glasslayer 501 and iris glass layer 502 and a border seal adhesive 521couples these two substrates together. In one embodiment, patch glasslayer 501 and iris glass layer 502 comprise glass layers, though theymay be other types of substrates.

Iris metal layer 541 is fabricated on top of iris layer 502. Passivationlayer 531 is fabricated on top of iris metal 541 and the iris layer 502where iris metal 541 is absent. Over passivation layer 531 comprisesheater bus metal 512. Over the passivation layer 531 that is over irismetal 541 is passivation layer 550. Heating wire 510 is fabricated ontop of passivation layer 550 and on top of a portion of heater bus metal512. In an alternative embodiment, there is a passivation layer betweenheater bus metal 512 and heating wire 510 with a via through thepassivation layer connecting heater bus metal 512 and heating wire 510.Passivation layer 530 is fabricated over heating wire 510 or at least aportion of heating wire 510, with alignment layer 540 on top ofpassivation layer 530. On patch layer 501, a passivation layer 532 isfabricated. On top of passivation layer 532 is a metallization 511supplying the heater bus. A passivation layer 530 covers a portion ofheater bus metal 511, while alignment layer 540 covers a portion ofpassivation layers 530 and is used for aligning LC 560. A bond/connectorstructure 513 is located to allow an electrical connection between theheater power bus and an external power supply (not shown).

Conductive cross-over 520 electrically connects the heater bus metal 511to heater bus metal 512 such that the power supply connected toconnector structure 513 is able to supply power through heater bus metal511 through the conductor cross-over 520 to heater bus metal 512 whichprovides the power to heating wire 510.

FIG. 6 illustrates one embodiment of a heater bus electrical cross-overfrom the iris layer to the patch layer within a border seal structure.Referring to FIG. 6, a conductive cross-over 620 is with the border seal621 and provides an electrical connection between the heater bus metal611 that is fabricated on the patch glass layer 601 to heater bus 612,which is on the iris glass layer 602. Heater wire 615 is fabricated on aportion of passivation layer 650 that is fabricated on top of iris metal641 and is fabricated onto a portion of heater bus metal 612. In analternative embodiment, there is a passivation layer between heater busmetal 612 and heating wire 615 with a via through the passivation layerconnecting heater bus metal 612 and heating wire 615.

A patch overhang has no facing iris glass outside the border seal. Aniris under hang has no facing patch glass outside the border seal.Metallization on an overhang or under hang is therefore accessible tomake a connection to the heater power supply/controller. For example,this connection might be made by an ACF (anisotropic conductiveadhesive) to a flex cable. This flex cable might connect to the heaterpower supply/controller. This heater power supply/controller might be onthe aperture controller board or might be an independent powersupply/controller unit.

Note that in the figures the patch glass, especially around the borderseal region, has a number of other structures on it besides this heaterwiring. The heater connection structures as drawn focus only on a methodof supplying the heaters, and do not try to show the integration withother patch structures, for example, the voltage bus that connects fromthe patch overhang to the iris metal. A layer of passivation above theheater supply metallization 511 (in FIG. 5) and 611 (in FIG. 6),isolates this heater supply metallization from the rest of the patchcircuitry.

Placement of the Heater Wiring, Heater Buses and Connections

The heater wiring and heater buses might be placed on either the patchglass side of the aperture, the iris glass side of the aperture, or havemay have parts on both patch and iris glass (or non-glass) layers of theaperture. The connection for the heaters may come out on the patch glasslayer or the iris glass layer side of the aperture.

Temperature Sensors Inside the RF Aperture

In one embodiment, one or more temperature sensors are located withinthe aperture. These temperature sensors are used to monitor the internalaperture temperature and to control whether the heater, including theheating elements (wires), heater buses and heater connections need to beengaged to regulate the temperature in the aperture. This may benecessary where the RF antenna elements need to be put in a certaintemperature or range of temperatures. For example, when each of the RFantenna elements includes an LC, the antenna element operates moreeffectively if the LC is at a certain temperature. Therefore, bymonitoring the temperature within the aperture and determining that thetemperature of the LC is below its optimal temperature range, theheating wires, buses and connections can be used to heat the internalaperture until the LC is at the desired temperature range.

Using an Antenna Element Control Transistor (e.g., TFT) for ApertureTemperature Measurement

Embodiments of the invention include techniques for using a transistor(e.g., a TFT) integrated onto the patch layer substrate to measure LCtemperature. In one embodiment, this technique uses the changingmobility characteristics of the TFT over temperature to indicate thetemperature.

FIGS. 7A-7C are typical TFT Voltage vs Current curves at differenttemperatures. Referring to FIGS. 7A-7C, each chart has a plot for twovalues of Vds where the vertical axis is Id, the horizontal axis is Vgs.

Note that Id for a given Vds and Vgs changes over temperature. By usingthis TFT characteristic and setting the Vgs and Vds to known constantvalues, the measured Id value can be correlated to the temperature ofthe TFT.

FIG. 8A is a flow diagram of one embodiment of a process for determiningan estimate of temperature of the LC using a TFT (or other type oftransistor). The TFT is connected to the LC. Therefore, the temperatureof the TFT provides an indication of the temperature of the LC. Theprocess is performed by a temperature control system that includes atemperature monitoring subsystem.

Referring to FIG. 8A, the process begins by adjusting a digital voltagevalue, referred to as the digital-to-analog converter (DAC) value, untilthe voltage Vgs measurement analog-to-digital converter (ADC) indicatesthe predefined Vgs value (processing block 801). Next, processing logicin the temperature control system measures the current Id by reading theId measurement ADC that is monitoring the voltage across a current senseresistor (processing block 802). Based on the Vgs voltage value and theId current value, processing logic correlates the Id value to thecalibrated temperature value (processing block 803). The correlation maybe performed by a correlator/processing unit (e.g., processor) thataccess a lookup table (LUT) using the values to determine acorresponding temperature value for the TFT.

FIG. 8B illustrates an example of a temperature measurement circuitry.Referring to FIG. 8B, a voltage value is provided by DAC 861 to acircuit having current sensor resistor 862 coupled in series with atransistor 864. In one embodiment, a transistor 864 is in contact withliquid crystal (LC) in the RF antenna element. In one embodiment,transistor 864 comprises a thin film transistor (TFT). In oneembodiment, the voltage value output from DAC 861 comes from atemperature controller 831. In one embodiment, a temperature adjustmentunit 843 may provide different voltage values based on the type oftransistor being monitored.

The voltage value across current sensor resistor 862 is monitored usingcomparator 863 to produce a current measurement that is converted todigital form by ADC 810. Based on the measurement current and themeasured Vgs voltage, correlator 841 determines the temperature 842 oftransistor 864 based on a correlation between transistor 864 and themeasured current Id and Vgs voltage (processing block 803). Sincetransistor 864 is in contact with the LC, the temperature of transistor864 is used to indicate or represent the temperature of the LC.

FIG. 8C is a flow diagram of one embodiment of a process for determiningan estimate of temperature of the LC using a TFT (or other type oftransistor) configured in a different manner than that of FIG. 8A. As inFIG. 8A, the TFT is connected to the LC and the temperature of the TFTprovides an indication of the temperature of the LC. The process isperformed by a temperature control system that includes a temperaturemonitoring subsystem.

Referring to FIG. 8C, the process begins by adjusting a digital voltagevalue, referred to as the digital-to-analog converter (DAC) value, untilthe voltage Vds measurement analog-to-digital converter (ADC) indicatesthe predefined Vds value (processing block 804). Next, processing logicin the temperature control system measures the current Id by reading theId measurement ADC that is monitoring the voltage across a current senseresistor (processing block 805). Based on the Vds voltage value and theId current value, processing logic correlates the Id value to thecalibrated temperature value (processing block 806). The correlation maybe performed by a correlator/processing unit (e.g., processor) thataccess a lookup table (LUT) using the values to determine acorresponding temperature value for the TFT.

FIG. 8D illustrates another example of a temperature monitoring circuitfor a TFT using the procedure of FIG. 8C. The circuit in FIG. 8D issubstantially similar to that of FIG. 8B with the exception thattransistor 814 is coupled in a different way. Thus, the measuring by themonitoring subsystem and the operation of temperature controller 831operates in the same way.

In one embodiment, multiple test TFTs can be distributed around the RFelements (and their LC) in the antenna array to measure the temperatureat various locations and/or for temperature averaging.

Using Capacitance Properties of the LC to Measure LC Temperature

In one embodiment, LC temperature is measured by using the capacitanceproperties of the LC. This uses the characteristic of the LC that theelectrical capacitance changes as a function of temperature.

In one embodiment, an electrical test capacitor is made by placing aconductive surface on the patch glass layer and a matching conductivesurface be placed on the iris glass layer, thereby creating a capacitorwith the LC acting as the separating dielectric material. Theseconductive surfaces are connected to circuitry that measures thecapacitance (such as a capacitance-to-digital converter (CDC)). Sincethe capacitance of the LC is a function of temperature, the capacitanceof the test capacitor can be correlated to the temperature of the LCdirectly.

FIG. 9 illustrates a circuit to determine the capacitance of the LC inorder to determine the temperature of the LC in the RF antenna elements.Referring to FIG. 9, an excitation signal 901 is provided to a conductor910D that connects iris glass layer 910E to liquid crystal 910C. In oneembodiment, the excitation is a square wave. In one embodiment, theexcitation signal 901 comes from a DAC with an input providedtemperature controller 931. In one embodiment, a temperature adjustmentunit 943 may provide different voltage values based on the type of testcapacitor being monitored.

Patch glass layer 910A is coupled to liquid crystal 910C using conductor910B. Applying the square wave of signal 901 to conductor 910D causes acapacitance to be created over liquid crystal 910C that is measured withΣ-Δ digital converter (CDC) 902. The output of CDC 902 is provided totemperature controller 931, which correlates the capacitancemeasurement, using correlator 941, to a temperature 942 of the LC of theLC-based test capacitor. This temperature is then used as thetemperature of the LCs in the RF antenna elements in the array.

In yet another embodiment, the temperature monitoring subsystem isoperable to measure decay speed of a liquid crystal and correlate thedecay speed to a temperature of the liquid crystal. The decay speed ofan LC is well-known in the art and the amount of time an LC is used iseasily tracked. In one embodiment, the correlation operation isperformed in the same manner as described above in conjunction withFIGS. 8B, 8D and 9.

In one embodiment, multiple test patches are distributed around theantenna array of RF LC-based antenna elements to measure the temperaturevarious location and/or for temperature averaging.

The heater, including the heater elements and heater buses, is operatedin conjunction with a temperature sensor to provide feedback to theheater system. The temperature sensor may be in the aperture or on theaperture. Some correlation of the temperature inside the aperture andthe temperature measured by the sensor may need to be established by acalibration procedure.

In one embodiment, the temperature of the aperture is regulated by acontrol loop consisting of the temperature sensor and the heater powersupply/controller. When the sensor indicates that the aperture is belowits operational temperature, the heater power controller causes theheater to turn on to heat the aperture. There are many methods by whichthe desired aperture temperature can be controlled using the heaterstructures described herein.

In an alternative embodiment, instead of placing the heater inside ofthe RF aperture, the same types of heater wire patterns, heater wirepattern placement, heater buses and heater bus placements are made on asuperstrate. In one embodiment, the superstrate is a substrate directlyon the satellite facing side of the RF aperture. In one embodiment, theimplementation is the same as is described above for use within the RFaperture (in the RF element/LC plane).

In one embodiment, when placing the heater on the superstrate, thesuperstrate is placed with the heater wire pattern between the top ofthe patch layer and the bottom of the superstrate, as close to the LClayer as possible. One potential problem with placing the heater on thesuperstrate is that the interaction of RF coming from the patch layerwith the heater wires on the superstrate may have a detrimental effecton the RF pattern being formed by the RF aperture. To reduce theinteraction of the RF with the heater wires, in one embodiment, thepatch layer is thinned as much as possible, to move the heater as closeto the RF element/LC plane as possible.

FIGS. 21A and 21B illustrate an example of a superstrate with a heaterpattern attached thereto. Referring to FIGS. 21A and 21B superstrate2101 includes a heater wire pattern 2103 on its bottom side. A heaterbus 2102 is also attached to the bottom of superstrate 2101. Superstrate2101 is coupled to segment 2100 that includes aperture area 2110 of RFantenna elements as shown in FIG. 21B, a patch overhang 2103.

Examples of Antenna Embodiments

The techniques described above may be used with flat panel antennas.Embodiments of such flat panel antennas are disclosed. The flat panelantennas include one or more arrays of antenna elements on an antennaaperture. In one embodiment, the antenna elements comprise liquidcrystal cells. In one embodiment, the flat panel antenna is acylindrically fed antenna that includes matrix drive circuitry touniquely address and drive each of the antenna elements that are notplaced in rows and columns. In one embodiment, the elements are placedin rings.

In one embodiment, the antenna aperture having the one or more arrays ofantenna elements is comprised of multiple segments coupled together.When coupled together, the combination of the segments form closedconcentric rings of antenna elements. In one embodiment, the concentricrings are concentric with respect to the antenna feed.

Overview of an Example of Antenna Systems

In one embodiment, the flat panel antenna is part of a metamaterialantenna system. Embodiments of a metamaterial antenna system forcommunications satellite earth stations are described. In oneembodiment, the antenna system is a component or subsystem of asatellite earth station (ES) operating on a mobile platform (e.g.,aeronautical, maritime, land, etc.) that operates using either Ka-bandfrequencies or Ku-band frequencies for civil commercial satellitecommunications. Note that embodiments of the antenna system also can beused in earth stations that are not on mobile platforms (e.g., fixed ortransportable earth stations).

In one embodiment, the antenna system uses surface scatteringmetamaterial technology to form and steer transmit and receive beamsthrough separate antennas. In one embodiment, the antenna systems areanalog systems, in contrast to antenna systems that employ digitalsignal processing to electrically form and steer beams (such as phasedarray antennas).

In one embodiment, the antenna system is comprised of three functionalsubsystems: (1) a wave guiding structure consisting of a cylindricalwave feed architecture; (2) an array of wave scattering metamaterialunit cells that are part of antenna elements; and (3) a controlstructure to command formation of an adjustable radiation field (beam)from the metamaterial scattering elements using holographic principles.

Examples of Wave Guiding Structures

FIG. 10 illustrates an aperture having one or more arrays of antennaelements placed in concentric rings around an input feed of thecylindrically fed antenna. In one embodiment, the cylindrically fedantenna includes a coaxial feed that is used to provide a cylindricalwave feed. In one embodiment, the cylindrical wave feed architecturefeeds the antenna from a central point with an excitation that spreadsoutward in a cylindrical manner from the feed point. That is, acylindrically fed antenna creates an outward travelling concentric feedwave. Even so, the shape of the cylindrical feed antenna around thecylindrical feed can be circular, square or any shape. In anotherembodiment, a cylindrically fed antenna creates an inward travellingfeed wave. In such a case, the feed wave most naturally comes from acircular structure.

Antenna Elements

In one embodiment, the antenna elements comprise a group of patchantennas. This group of patch antennas comprises an array of scatteringmetamaterial elements. In one embodiment, each scattering element in theantenna system is part of a unit cell that consists of a lowerconductor, a dielectric substrate and an upper conductor that embeds acomplementary electric inductive-capacitive resonator (“complementaryelectric LC” or “CELC”) that is etched in or deposited onto the upperconductor. As would be understood by those skilled in the art, LC in thecontext of CELC refers to inductance-capacitance, as opposed to liquidcrystal.

In one embodiment, a liquid crystal (LC) is disposed in the gap aroundthe scattering element. This LC is driven by the direct driveembodiments described above. In one embodiment, liquid crystal isencapsulated in each unit cell and separates the lower conductorassociated with a slot from an upper conductor associated with itspatch. Liquid crystal has a permittivity that is a function of theorientation of the molecules comprising the liquid crystal, and theorientation of the molecules (and thus the permittivity) can becontrolled by adjusting the bias voltage across the liquid crystal.Using this property, in one embodiment, the liquid crystal integrates anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna. Note that the teachings herein arenot limited to having a liquid crystal that operates in a binary fashionwith respect to energy transmission.

In one embodiment, the feed geometry of this antenna system allows theantenna elements to be positioned at forty five degree (45°) angles tothe vector of the wave in the wave feed. Note that other positions maybe used (e.g., at 40° angles). This position of the elements enablescontrol of the free space wave received by or transmitted/radiated fromthe elements. In one embodiment, the antenna elements are arranged withan inter-element spacing that is less than a free-space wavelength ofthe operating frequency of the antenna. For example, if there are fourscattering elements per wavelength, the elements in the 30 GHz transmitantenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-spacewavelength of 30 GHz).

In one embodiment, the two sets of elements are perpendicular to eachother and simultaneously have equal amplitude excitation if controlledto the same tuning state. Rotating them +/−45 degrees relative to thefeed wave excitation achieves both desired features at once. Rotatingone set 0 degrees and the other 90 degrees would achieve theperpendicular goal, but not the equal amplitude excitation goal. Notethat 0 and 90 degrees may be used to achieve isolation when feeding thearray of antenna elements in a single structure from two sides.

The amount of radiated power from each unit cell is controlled byapplying a voltage to the patch (potential across the LC channel) usinga controller. Traces to each patch are used to provide the voltage tothe patch antenna. The voltage is used to tune or detune the capacitanceand thus the resonance frequency of individual elements to effectuatebeam forming. The voltage required is dependent on the liquid crystalmixture being used. The voltage tuning characteristic of liquid crystalmixtures is mainly described by a threshold voltage at which the liquidcrystal starts to be affected by the voltage and the saturation voltage,above which an increase of the voltage does not cause major tuning inliquid crystal. These two characteristic parameters can change fordifferent liquid crystal mixtures.

In one embodiment, as discussed above, a matrix drive is used to applyvoltage to the patches in order to drive each cell separately from allthe other cells without having a separate connection for each cell(direct drive). Because of the high density of elements, the matrixdrive is an efficient way to address each cell individually.

In one embodiment, the control structure for the antenna system has 2main components: the antenna array controller, which includes driveelectronics, for the antenna system, is below the wave scatteringstructure, while the matrix drive switching array is interspersedthroughout the radiating RF array in such a way as to not interfere withthe radiation. In one embodiment, the drive electronics for the antennasystem comprise commercial off-the shelf LCD controls used in commercialtelevision appliances that adjust the bias voltage for each scatteringelement by adjusting the amplitude or duty cycle of an AC bias signal tothat element.

In one embodiment, the antenna array controller also contains amicroprocessor executing the software. The control structure may alsoincorporate sensors (e.g., a GPS receiver, a three axis compass, a3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, etc.) to providelocation and orientation information to the processor. The location andorientation information may be provided to the processor by othersystems in the earth station and/or may not be part of the antennasystem.

More specifically, the antenna array controller controls which elementsare turned off and those elements turned on and at which phase andamplitude level at the frequency of operation. The elements areselectively detuned for frequency operation by voltage application.

For transmission, a controller supplies an array of voltage signals tothe RF patches to create a modulation, or control pattern. The controlpattern causes the elements to be turned to different states. In oneembodiment, multistate control is used in which various elements areturned on and off to varying levels, further approximating a sinusoidalcontrol pattern, as opposed to a square wave (i.e., a sinusoid grayshade modulation pattern). In one embodiment, some elements radiate morestrongly than others, rather than some elements radiate and some do not.Variable radiation is achieved by applying specific voltage levels,which adjusts the liquid crystal permittivity to varying amounts,thereby detuning elements variably and causing some elements to radiatemore than others.

The generation of a focused beam by the metamaterial array of elementscan be explained by the phenomenon of constructive and destructiveinterference. Individual electromagnetic waves sum up (constructiveinterference) if they have the same phase when they meet in free spaceand waves cancel each other (destructive interference) if they are inopposite phase when they meet in free space. If the slots in a slottedantenna are positioned so that each successive slot is positioned at adifferent distance from the excitation point of the guided wave, thescattered wave from that element will have a different phase than thescattered wave of the previous slot. If the slots are spaced one quarterof a guided wavelength apart, each slot will scatter a wave with a onefourth phase delay from the previous slot.

Using the array, the number of patterns of constructive and destructiveinterference that can be produced can be increased so that beams can bepointed theoretically in any direction plus or minus ninety degrees(90°) from the bore sight of the antenna array, using the principles ofholography. Thus, by controlling which metamaterial unit cells areturned on or off (i.e., by changing the pattern of which cells areturned on and which cells are turned off), a different pattern ofconstructive and destructive interference can be produced, and theantenna can change the direction of the main beam. The time required toturn the unit cells on and off dictates the speed at which the beam canbe switched from one location to another location.

In one embodiment, the antenna system produces one steerable beam forthe uplink antenna and one steerable beam for the downlink antenna. Inone embodiment, the antenna system uses metamaterial technology toreceive beams and to decode signals from the satellite and to formtransmit beams that are directed toward the satellite. In oneembodiment, the antenna systems are analog systems, in contrast toantenna systems that employ digital signal processing to electricallyform and steer beams (such as phased array antennas). In one embodiment,the antenna system is considered a “surface” antenna that is planar andrelatively low profile, especially when compared to conventionalsatellite dish receivers.

FIG. 11 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.Reconfigurable resonator layer 1230 includes an array of tunable slots1210. The array of tunable slots 1210 can be configured to point theantenna in a desired direction. Each of the tunable slots can betuned/adjusted by varying a voltage across the liquid crystal.

Control module 1280 is coupled to reconfigurable resonator layer 1230 tomodulate the array of tunable slots 1210 by varying the voltage acrossthe liquid crystal in FIG. 11. Control module 1280 may include a FieldProgrammable Gate Array (“FPGA”), a microprocessor, a controller,System-on-a-Chip (SoC), or other processing logic. In one embodiment,control module 1280 includes logic circuitry (e.g., multiplexer) todrive the array of tunable slots 1210. In one embodiment, control module1280 receives data that includes specifications for a holographicdiffraction pattern to be driven onto the array of tunable slots 1210.The holographic diffraction patterns may be generated in response to aspatial relationship between the antenna and a satellite so that theholographic diffraction pattern steers the downlink beams (and uplinkbeam if the antenna system performs transmit) in the appropriatedirection for communication. Although not drawn in each figure, acontrol module similar to control module 1280 may drive each array oftunable slots described in the figures of the disclosure.

Radio Frequency (“RF”) holography is also possible using analogoustechniques where a desired RF beam can be generated when an RF referencebeam encounters an RF holographic diffraction pattern. In the case ofsatellite communications, the reference beam is in the form of a feedwave, such as feed wave 1205 (approximately 20 GHz in some embodiments).To transform a feed wave into a radiated beam (either for transmittingor receiving purposes), an interference pattern is calculated betweenthe desired RF beam (the object beam) and the feed wave (the referencebeam). The interference pattern is driven onto the array of tunableslots 1210 as a diffraction pattern so that the feed wave is “steered”into the desired RF beam (having the desired shape and direction). Inother words, the feed wave encountering the holographic diffractionpattern “reconstructs” the object beam, which is formed according todesign requirements of the communication system. The holographicdiffraction pattern contains the excitation of each element and iscalculated by w_(hologram)=w_(in)*w_(out), with w_(in) as the waveequation in the waveguide and w_(out) the wave equation on the outgoingwave.

FIG. 12 illustrates one embodiment of a tunable resonator/slot 1210.Tunable slot 1210 includes an iris/slot 1212, a radiating patch 1211,and liquid crystal 1213 disposed between iris 1212 and patch 1211. Inone embodiment, radiating patch 1211 is co-located with iris 1212.

FIG. 13 illustrates a cross section view of one embodiment of a physicalantenna aperture. The antenna aperture includes ground plane 1245, and ametal layer 1236 within iris layer 1233, which is included inreconfigurable resonator layer 1230. In one embodiment, the antennaaperture of FIG. 13 includes a plurality of tunable resonator/slots 1210of FIG. 12. Iris/slot 1212 is defined by openings in metal layer 1236. Afeed wave, such as feed wave 1205 of FIG. 11, may have a microwavefrequency compatible with satellite communication channels. The feedwave propagates between ground plane 1245 and resonator layer 1230.

Reconfigurable resonator layer 1230 also includes gasket layer 1232 andpatch layer 1231. Gasket layer 1232 is disposed below patch layer 1231and iris layer 1233. Note that in one embodiment, a spacer could replacegasket layer 1232. In one embodiment, iris layer 1233 is a printedcircuit board (“PCB”) that includes a copper layer as metal layer 1236.In one embodiment, iris layer 1233 is glass. Iris layer 1233 may beother types of substrates.

Openings may be etched in the copper layer to form slots 1212. In oneembodiment, iris layer 1233 is conductively coupled by a conductivebonding layer to another structure (e.g., a waveguide) in FIG. 13. Notethat in an embodiment the iris layer is not conductively coupled by aconductive bonding layer and is instead interfaced with a non-conductingbonding layer.

Patch layer 1231 may also be a PCB that includes metal as radiatingpatches 1211. In one embodiment, gasket layer 1232 includes spacers 1239that provide a mechanical standoff to define the dimension between metallayer 1236 and patch 1211. In one embodiment, the spacers are 75microns, but other sizes may be used (e.g., 3-200 mm). As mentionedabove, in one embodiment, the antenna aperture of FIG. 13 includesmultiple tunable resonator/slots, such as tunable resonator/slot 1210includes patch 1211, liquid crystal 1213, and iris 1212 of FIG. 12. Thechamber for liquid crystal 1213 is defined by spacers 1239, iris layer1233 and metal layer 1236. When the chamber is filled with liquidcrystal, patch layer 1231 can be laminated onto spacers 1239 to sealliquid crystal within resonator layer 1230.

A voltage between patch layer 1231 and iris layer 1233 can be modulatedto tune the liquid crystal in the gap between the patch and the slots(e.g., tunable resonator/slot 1210). Adjusting the voltage across liquidcrystal 1213 varies the capacitance of a slot (e.g., tunableresonator/slot 1210). Accordingly, the reactance of a slot (e.g.,tunable resonator/slot 1210) can be varied by changing the capacitance.Resonant frequency of slot 1210 also changes according to the equationf=1/2π√{square root over (LC)} where f is the resonant frequency of slot1210 and L and C are the inductance and capacitance of slot 1210,respectively. The resonant frequency of slot 1210 affects the energyradiated from feed wave 1205 propagating through the waveguide. As anexample, if fed wave 1205 is 20 GHz, the resonant frequency of a slot1210 may be adjusted (by varying the capacitance) to 17 GHz so that theslot 1210 couples substantially no energy from feed wave 1205. Or, theresonant frequency of a slot 1210 may be adjusted to 20 GHz so that theslot 1210 couples energy from feed wave 1205 and radiates that energyinto free space. Although the examples given are binary (fully radiatingor not radiating at all), full gray scale control of the reactance, andtherefore the resonant frequency of slot 1210 is possible with voltagevariance over a multi-valued range. Hence, the energy radiated from eachslot 1210 can be finely controlled so that detailed holographicdiffraction patterns can be formed by the array of tunable slots.

In one embodiment, tunable slots in a row are spaced from each other byλ/5. Other spacings may be used. In one embodiment, each tunable slot ina row is spaced from the closest tunable slot in an adjacent row by λ/2,and, thus, commonly oriented tunable slots in different rows are spacedby λ/4, though other spacings are possible (e.g., λ/5, λ/6.3). Inanother embodiment, each tunable slot in a row is spaced from theclosest tunable slot in an adjacent row by λ/3.

Embodiments use reconfigurable metamaterial technology, such asdescribed in U.S. patent application Ser. No. 14/550,178, entitled“Dynamic Polarization and Coupling Control from a SteerableCylindrically Fed Holographic Antenna”, filed Nov. 21, 2014 and U.S.patent application Ser. No. 14/610,502, entitled “Ridged Waveguide FeedStructures for Reconfigurable Antenna”, filed Jan. 30, 2015.

FIGS. 14A-D illustrate one embodiment of the different layers forcreating the slotted array. The antenna array includes antenna elementsthat are positioned in rings, such as the example rings shown in FIG.10. Note that in this example the antenna array has two different typesof antenna elements that are used for two different types of frequencybands.

FIG. 14A illustrates a portion of the first iris board layer withlocations corresponding to the slots. Referring to FIG. 14A, the circlesare open areas/slots in the metallization in the bottom side of the irissubstrate, and are for controlling the coupling of elements to the feed(the feed wave). Note that this layer is an optional layer and is notused in all designs. FIG. 14B illustrates a portion of the second irisboard layer containing slots. FIG. 14C illustrates patches over aportion of the second iris board layer. FIG. 14D illustrates a top viewof a portion of the slotted array.

FIG. 15 illustrates a side view of one embodiment of a cylindrically fedantenna structure. The antenna produces an inwardly travelling waveusing a double layer feed structure (i.e., two layers of a feedstructure). In one embodiment, the antenna includes a circular outershape, though this is not required. That is, non-circular inwardtravelling structures can be used. In one embodiment, the antennastructure in FIG. 15 includes the coaxial feed of FIG. 9.

Referring to FIG. 15, a coaxial pin 1601 is used to excite the field onthe lower level of the antenna. In one embodiment, coaxial pin 1601 is a50Ω coax pin that is readily available. Coaxial pin 1601 is coupled(e.g., bolted) to the bottom of the antenna structure, which isconducting ground plane 1602.

Separate from conducting ground plane 1602 is interstitial conductor1603, which is an internal conductor. In one embodiment, conductingground plane 1602 and interstitial conductor 1603 are parallel to eachother. In one embodiment, the distance between ground plane 1602 andinterstitial conductor 1603 is 0.1-0.15″. In another embodiment, thisdistance may be λ/2, where λ is the wavelength of the travelling wave atthe frequency of operation.

Ground plane 1602 is separated from interstitial conductor 1603 via aspacer 1604. In one embodiment, spacer 1604 is a foam or air-likespacer. In one embodiment, spacer 1604 comprises a plastic spacer.

On top of interstitial conductor 1603 is dielectric layer 1605. In oneembodiment, dielectric layer 1605 is plastic. The purpose of dielectriclayer 1605 is to slow the travelling wave relative to free spacevelocity. In one embodiment, dielectric layer 1605 slows the travellingwave by 30% relative to free space. In one embodiment, the range ofindices of refraction that are suitable for beam forming are 1.2-1.8,where free space has by definition an index of refraction equal to 1.Other dielectric spacer materials, such as, for example, plastic, may beused to achieve this effect. Note that materials other than plastic maybe used as long as they achieve the desired wave slowing effect.Alternatively, a material with distributed structures may be used asdielectric 1605, such as periodic sub-wavelength metallic structuresthat can be machined or lithographically defined, for example.

An RF-array 1606 is on top of dielectric 1605. In one embodiment, thedistance between interstitial conductor 1603 and RF-array 1606 is0.1-0.15″. In another embodiment, this distance may be λ_(eff)/2, whereλ_(eff) is the effective wavelength in the medium at the designfrequency.

The antenna includes sides 1607 and 1608. Sides 1607 and 1608 are angledto cause a travelling wave feed from coax pin 1601 to be propagated fromthe area below interstitial conductor 1603 (the spacer layer) to thearea above interstitial conductor 1603 (the dielectric layer) viareflection. In one embodiment, the angle of sides 1607 and 1608 are at45° angles. In an alternative embodiment, sides 1607 and 1608 could bereplaced with a continuous radius to achieve the reflection. While FIG.15 shows angled sides that have angle of 45 degrees, other angles thataccomplish signal transmission from lower level feed to upper level feedmay be used. That is, given that the effective wavelength in the lowerfeed will generally be different than in the upper feed, some deviationfrom the ideal 45° angles could be used to aid transmission from thelower to the upper feed level. For example, in another embodiment, the45° angles are replaced with a single step. The steps on one end of theantenna go around the dielectric layer, interstitial the conductor, andthe spacer layer. The same two steps are at the other ends of theselayers.

In operation, when a feed wave is fed in from coaxial pin 1601, the wavetravels outward concentrically oriented from coaxial pin 1601 in thearea between ground plane 1602 and interstitial conductor 1603. Theconcentrically outgoing waves are reflected by sides 1607 and 1608 andtravel inwardly in the area between interstitial conductor 1603 and RFarray 1606. The reflection from the edge of the circular perimetercauses the wave to remain in phase (i.e., it is an in-phase reflection).The travelling wave is slowed by dielectric layer 1605. At this point,the travelling wave starts interacting and exciting with elements in RFarray 1606 to obtain the desired scattering.

To terminate the travelling wave, a termination 1609 is included in theantenna at the geometric center of the antenna. In one embodiment,termination 1609 comprises a pin termination (e.g., a 50Ω pin). Inanother embodiment, termination 1609 comprises an RF absorber thatterminates unused energy to prevent reflections of that unused energyback through the feed structure of the antenna. These could be used atthe top of RF array 1606.

FIG. 16 illustrates another embodiment of the antenna system with anoutgoing wave. Referring to FIG. 16, two ground planes 1610 and 1611 aresubstantially parallel to each other with a dielectric layer 1612 (e.g.,a plastic layer, etc.) in between ground planes. RF absorbers 1619(e.g., resistors) couple the two ground planes 1610 and 1611 together. Acoaxial pin 1615 (e.g., 50Ω) feeds the antenna. An RF array 1616 is ontop of dielectric layer 1612 and ground plane 1611.

In operation, a feed wave is fed through coaxial pin 1615 and travelsconcentrically outward and interacts with the elements of RF array 1616.

The cylindrical feed in both the antennas of FIGS. 15 and 16 improvesthe service angle of the antenna. Instead of a service angle of plus orminus forty five degrees azimuth (±45° Az) and plus or minus twenty fivedegrees elevation (±25° El), in one embodiment, the antenna system has aservice angle of seventy five degrees (75°) from the bore sight in alldirections. As with any beam forming antenna comprised of manyindividual radiators, the overall antenna gain is dependent on the gainof the constituent elements, which themselves are angle-dependent. Whenusing common radiating elements, the overall antenna gain typicallydecreases as the beam is pointed further off bore sight. At 75 degreesoff bore sight, significant gain degradation of about 6 dB is expected.

Embodiments of the antenna having a cylindrical feed solve one or moreproblems. These include dramatically simplifying the feed structurecompared to antennas fed with a corporate divider network and thereforereducing total required antenna and antenna feed volume; decreasingsensitivity to manufacturing and control errors by maintaining high beamperformance with coarser controls (extending all the way to simplebinary control); giving a more advantageous side lobe pattern comparedto rectilinear feeds because the cylindrically oriented feed wavesresult in spatially diverse side lobes in the far field; and allowingpolarization to be dynamic, including allowing left-hand circular,right-hand circular, and linear polarizations, while not requiring apolarizer.

Array of Wave Scattering Elements

RF array 1606 of FIG. 15 and RF array 1616 of FIG. 16 include a wavescattering subsystem that includes a group of patch antennas (i.e.,scatterers) that act as radiators. This group of patch antennascomprises an array of scattering metamaterial elements.

In one embodiment, each scattering element in the antenna system is partof a unit cell that consists of a lower conductor, a dielectricsubstrate and an upper conductor that embeds a complementary electricinductive-capacitive resonator (“complementary electric LC” or “CELC”)that is etched in or deposited onto the upper conductor.

In one embodiment, a liquid crystal (LC) is injected in the gap aroundthe scattering element. Liquid crystal is encapsulated in each unit celland separates the lower conductor associated with a slot from an upperconductor associated with its patch. Liquid crystal has a permittivitythat is a function of the orientation of the molecules comprising theliquid crystal, and the orientation of the molecules (and thus thepermittivity) can be controlled by adjusting the bias voltage across theliquid crystal. Using this property, the liquid crystal acts as anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna.

Controlling the thickness of the LC increases the beam switching speed.A fifty percent (50%) reduction in the gap between the lower and theupper conductor (the thickness of the liquid crystal) results in afourfold increase in speed. In another embodiment, the thickness of theliquid crystal results in a beam switching speed of approximatelyfourteen milliseconds (14 ms). In one embodiment, the LC is doped in amanner well-known in the art to improve responsiveness so that a sevenmillisecond (7 ms) requirement can be met.

The CELC element is responsive to a magnetic field that is appliedparallel to the plane of the CELC element and perpendicular to the CELCgap complement. When a voltage is applied to the liquid crystal in themetamaterial scattering unit cell, the magnetic field component of theguided wave induces a magnetic excitation of the CELC, which, in turn,produces an electromagnetic wave in the same frequency as the guidedwave.

The phase of the electromagnetic wave generated by a single CELC can beselected by the position of the CELC on the vector of the guided wave.Each cell generates a wave in phase with the guided wave parallel to theCELC. Because the CELCs are smaller than the wave length, the outputwave has the same phase as the phase of the guided wave as it passesbeneath the CELC.

In one embodiment, the cylindrical feed geometry of this antenna systemallows the CELC elements to be positioned at forty five degree (45°)angles to the vector of the wave in the wave feed. This position of theelements enables control of the polarization of the free space wavegenerated from or received by the elements. In one embodiment, the CELCsare arranged with an inter-element spacing that is less than afree-space wavelength of the operating frequency of the antenna. Forexample, if there are four scattering elements per wavelength, theelements in the 30 GHz transmit antenna will be approximately 2.5 mm(i.e., ¼th the 10 mm free-space wavelength of 30 GHz).

In one embodiment, the CELCs are implemented with patch antennas thatinclude a patch co-located over a slot with liquid crystal between thetwo. In this respect, the metamaterial antenna acts like a slotted(scattering) wave guide. With a slotted wave guide, the phase of theoutput wave depends on the location of the slot in relation to theguided wave.

Cell Placement

In one embodiment, the antenna elements are placed on the cylindricalfeed antenna aperture in a way that allows for a systematic matrix drivecircuit. The placement of the cells includes placement of thetransistors for the matrix drive. FIG. 17 illustrates one embodiment ofthe placement of matrix drive circuitry with respect to antennaelements. Referring to FIG. 17, row controller 1701 is coupled totransistors 1711 and 1712, via row select signals Row1 and Row2,respectively, and column controller 1702 is coupled to transistors 1711and 1712 via column select signal Column1. Transistor 1711 is alsocoupled to antenna element 1721 via connection to patch 1731, whiletransistor 1712 is coupled to antenna element 1722 via connection topatch 1732.

In an initial approach to realize matrix drive circuitry on thecylindrical feed antenna with unit cells placed in a non-regular grid,two steps are performed. In the first step, the cells are placed onconcentric rings and each of the cells is connected to a transistor thatis placed beside the cell and acts as a switch to drive each cellseparately. In the second step, the matrix drive circuitry is built inorder to connect every transistor with a unique address as the matrixdrive approach requires. Because the matrix drive circuit is built byrow and column traces (similar to LCDs) but the cells are placed onrings, there is no systematic way to assign a unique address to eachtransistor. This mapping problem results in very complex circuitry tocover all the transistors and leads to a significant increase in thenumber of physical traces to accomplish the routing. Because of the highdensity of cells, those traces disturb the RF performance of the antennadue to coupling effect. Also, due to the complexity of traces and highpacking density, the routing of the traces cannot be accomplished bycommercially available layout tools.

In one embodiment, the matrix drive circuitry is predefined before thecells and transistors are placed. This ensures a minimum number oftraces that are necessary to drive all the cells, each with a uniqueaddress. This strategy reduces the complexity of the drive circuitry andsimplifies the routing, which subsequently improves the RF performanceof the antenna.

More specifically, in one approach, in the first step, the cells areplaced on a regular rectangular grid composed of rows and columns thatdescribe the unique address of each cell. In the second step, the cellsare grouped and transformed to concentric circles while maintainingtheir address and connection to the rows and columns as defined in thefirst step. A goal of this transformation is not only to put the cellson rings but also to keep the distance between cells and the distancebetween rings constant over the entire aperture. In order to accomplishthis goal, there are several ways to group the cells.

In one embodiment, a TFT package is used to enable placement and uniqueaddressing in the matrix drive. FIG. 18 illustrates one embodiment of aTFT package. Referring to FIG. 18, a TFT and a hold capacitor 1803 isshown with input and output ports. There are two input ports connectedto traces 1801 and two output ports connected to traces 1802 to connectthe TFTs together using the rows and columns. In one embodiment, the rowand column traces cross in 90° angles to reduce, and potentiallyminimize, the coupling between the row and column traces. In oneembodiment, the row and column traces are on different layers.

An Example System Embodiment

In one embodiment, the combined antenna apertures are used in atelevision system that operates in conjunction with a set top box. Forexample, in the case of a dual reception antenna, satellite signalsreceived by the antenna are provided to a set top box (e.g., a DirecTVreceiver) of a television system. More specifically, the combinedantenna operation is able to simultaneously receive RF signals at twodifferent frequencies and/or polarizations. That is, one sub-array ofelements is controlled to receive RF signals at one frequency and/orpolarization, while another sub-array is controlled to receive signalsat another, different frequency and/or polarization. These differencesin frequency or polarization represent different channels being receivedby the television system. Similarly, the two antenna arrays can becontrolled for two different beam positions to receive channels from twodifferent locations (e.g., two different satellites) to simultaneouslyreceive multiple channels.

FIG. 19 is a block diagram of one embodiment of a communication systemthat performs dual reception simultaneously in a television system.Referring to FIG. 19, antenna 1401 includes two spatially interleavedantenna apertures operable independently to perform dual receptionsimultaneously at different frequencies and/or polarizations asdescribed above. Note that while only two spatially interleaved antennaoperations are mentioned, the TV system may have more than two antennaapertures (e.g., 3, 4, 5, etc. antenna apertures).

In one embodiment, antenna 1401, including its two interleaved slottedarrays, is coupled to diplexer 1430. The coupling may include one ormore feeding networks that receive the signals from elements of the twoslotted arrays to produce two signals that are fed into diplexer 1430.In one embodiment, diplexer 1430 is a commercially available diplexer(e.g., model PB1081WA Ku-band sitcom diplexer from A1 Microwave).

Diplexer 1430 is coupled to a pair of low noise block down converters(LNBs) 1426 and 1427, which perform a noise filtering function, a downconversion function, and amplification in a manner well-known in theart. In one embodiment, LNBs 1426 and 1427 are in an out-door unit(ODU). In another embodiment, LNBs 1426 and 1427 are integrated into theantenna apparatus. LNBs 1426 and 1427 are coupled to a set top box 1402,which is coupled to television 1403.

Set top box 1402 includes a pair of analog-to-digital converters (ADCs)1421 and 1422, which are coupled to LNBs 1426 and 1427, to convert thetwo signals output from diplexer 1430 into digital format.

Once converted to digital format, the signals are demodulated bydemodulator 1423 and decoded by decoder 1424 to obtain the encoded dataon the received waves. The decoded data is then sent to controller 1425,which sends it to television 1403.

Controller 1450 controls antenna 1401, including the interleaved slottedarray elements of both antenna apertures on the single combined physicalaperture.

An Example of a Full Duplex Communication System

In another embodiment, the combined antenna apertures are used in a fullduplex communication system. FIG. 20 is a block diagram of anotherembodiment of a communication system having simultaneous transmit andreceive paths. While only one transmit path and one receive path areshown, the communication system may include more than one transmit pathand/or more than one receive path.

Referring to FIG. 20, antenna 1401 includes two spatially interleavedantenna arrays operable independently to transmit and receivesimultaneously at different frequencies as described above. In oneembodiment, antenna 1401 is coupled to diplexer 1445. The coupling maybe by one or more feeding networks. In one embodiment, in the case of aradial feed antenna, diplexer 1445 combines the two signals and theconnection between antenna 1401 and diplexer 1445 is a single broad-bandfeeding network that can carry both frequencies.

Diplexer 1445 is coupled to a low noise block down converter (LNBs)1427, which performs a noise filtering function and a down conversionand amplification function in a manner well-known in the art. In oneembodiment, LNB 1427 is in an out-door unit (ODU). In anotherembodiment, LNB 1427 is integrated into the antenna apparatus. LNB 1427is coupled to a modem 1460, which is coupled to computing system 1440(e.g., a computer system, modem, etc.).

Modem 1460 includes an analog-to-digital converter (ADC) 1422, which iscoupled to LNB 1427, to convert the received signal output from diplexer1445 into digital format. Once converted to digital format, the signalis demodulated by demodulator 1423 and decoded by decoder 1424 to obtainthe encoded data on the received wave. The decoded data is then sent tocontroller 1425, which sends it to computing system 1440.

Modem 1460 also includes an encoder 1430 that encodes data to betransmitted from computing system 1440. The encoded data is modulated bymodulator 1431 and then converted to analog by digital-to-analogconverter (DAC) 1432. The analog signal is then filtered by a BUC(up-convert and high pass amplifier) 1433 and provided to one port ofdiplexer 1445. In one embodiment, BUC 1433 is in an out-door unit (ODU).

Diplexer 1445 operating in a manner well-known in the art provides thetransmit signal to antenna 1401 for transmission.

Controller 1450 controls antenna 1401, including the two arrays ofantenna elements on the single combined physical aperture.

Note that the full duplex communication system shown in FIG. 20 has anumber of applications, including but not limited to, internetcommunication, vehicle communication (including software updating), etc.

Some portions of the detailed descriptions above are presented in termsof algorithms and symbolic representations of operations on data bitswithin a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; etc.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asessential to the invention.

We claim:
 1. An antenna comprising: a physical antenna aperture havingan array of radio frequency (RF) antenna elements; and a plurality ofheating elements, each heating element being between pairs of RFelements of the array of RF elements.
 2. The antenna defined in claim 1wherein heating elements in the plurality of heating elements aresubstantially equidistant between RF antenna elements in the array. 3.The antenna defined in claim 1 wherein heating elements in the pluralityof heating elements are substantially midway between rings of iris/patchantenna elements.
 4. The antenna defined in claim 1 wherein heatingelements in the plurality of heating elements are in rings between theRF antenna elements.
 5. The antenna defined in claim 1 wherein theplurality of heating elements are wires.
 6. The antenna defined in claim5 wherein a majority of the wires are of equal length with crosssections that are similar in dimension over the length of the heatingwires.
 7. The antenna defined in claim 6 wherein the plurality of wiresprovides a same power dissipation per unit area over the antennaaperture.
 8. The antenna defined in claim 5 wherein heating wires areevenly distributed over the antenna aperture area.
 9. The antennadefined in claim 5 wherein width and height of a wire cross section ofthe heating wires varies over the antenna aperture while having a samepower dissipation per unit area.
 10. The antenna defined in claim 5further comprising heater power buses electrically connected to supplypower to the heating wires, wherein one or more heater power buses aretraverse through a border seal structure of the aperture.
 11. Theantenna defined in claim 10 wherein the one or more heater power busesare electrically connected to a metal layer on an iris layer or a patchlayer.
 12. The antenna defined in claim 1 further comprising atemperature monitoring subsystem to monitor temperature of RF antennaelements and control the plurality of heating elements to adjust thetemperature of the RF antenna elements.
 13. The antenna defined in claim12 wherein the temperature monitoring subsystem is operable to estimatea liquid crystal temperature of liquid crystal in the RF antennaelements.
 14. The antenna defined in claim 13 wherein the temperaturemonitoring subsystem comprises: one or more circuits comprising avoltage input, a current sense resistor and a transistor coupled inseries wherein the transistor is integrated onto a patch layer in theantenna and in contact with liquid crystal; a temperature controller toprovide an input voltage to the circuit; and a monitoring circuit tomonitor voltage across the current sense resistor to obtain a measuredcurrent, wherein the temperature controller is operable to correlate themeasured current to temperature of the transistor, the temperature ofthe transistor being indicative of the liquid crystal temperature. 15.The antenna defined in claim 13 wherein the temperature monitoringsubsystem is operable to measure the liquid crystal temperature bymonitoring a voltage across a current sense resistor that is coupled inseries with a transistor integrated onto a layer in the antenna and incontract with the liquid crystal, measuring the current through thecurrent sense resistor, and correlating the current to the transistortemperature, the temperature of the transistor being indicative of theliquid crystal temperature.
 16. The antenna defined in claim 15 whereinthe layer is a patch layer having a plurality of patches, wherein eachof the patches is co-located over and separated from a slot in aplurality of slots, forming a patch/slot pair.
 17. The antenna definedin claim 13 wherein the temperature monitoring subsystem is operable tomeasure capacitance of a capacitor by matching conductive surfaces onthe patch and iris layers in the aperture with liquid crystaltherebetween, measuring capacitance of the capacitor with a circuitcoupled to the conductive surfaces, and correlating the capacitance totemperature of the liquid crystal.
 18. The antenna defined in claim 13wherein the temperature monitoring subsystem is operable to measuredecay speed of a liquid crystal and correlate the decay speed to atemperature of the liquid crystal.
 19. The antenna defined in claim 1wherein the heating elements are part of a heater wire pattern on asuperstrate between the patch substrate and a bottom of the superstrate.20. The apparatus defined in claim 1 wherein the array of RF antennaelements comprises a tunable slotted array of antenna elements.
 21. Theapparatus defined in claim 20 wherein the tunable slotted arraycomprises: a plurality of slots; a plurality of patches, wherein each ofthe patches is co-located over and separated from a slot in theplurality of slots, forming a patch/slot pair, each patch/slot pairbeing turned off or on based on application of a voltage to the patch inthe pair; and a controller to apply a control pattern to control whichpatch/slot pairs are on and off to cause generation of a beam.
 22. Anantenna comprising: a physical antenna aperture having an array of radiofrequency (RF) antenna elements; a plurality of heating elements withinthe antenna aperture; and a temperature monitoring subsystem to monitortemperature within the antenna aperture and control the plurality ofheating elements to adjust the temperature of the RF antenna elements.23. The antenna defined in claim 21 wherein the temperature monitoringsubsystem is operable to estimate a liquid crystal temperature of liquidcrystal in the RF antenna elements.
 24. The antenna defined in claim 23wherein the temperature monitoring subsystem comprises: one or morecircuits comprising a voltage input, a current sense resistor and atransistor coupled in series wherein the transistor is integrated onto apatch layer in the antenna and in contact with liquid crystal; atemperature controller to provide an input voltage to the circuit; and amonitoring circuit to monitor voltage across the current sense resistorto obtain a measured current, wherein the temperature controller isoperable to correlate the measured current to temperature of thetransistor, the temperature of the transistor being indicative of theliquid crystal temperature.
 25. The antenna defined in claim 23 whereinthe temperature monitoring subsystem is operable to measure the liquidcrystal temperature by monitoring a voltage across a current senseresistor that is coupled in series with a transistor integrated onto alayer in the antenna and in contract with the liquid crystal, measuringthe current through the current sense resister, and correlating thecurrent to the transistor temperature, the temperature of the transistorbeing indicative of the liquid crystal temperature.
 26. The antennadefined in claim 25 wherein the layer is a patch layer having aplurality of patches, wherein each of the patches is co-located over andseparated from a slot in a plurality of slots, forming a patch/slotpair.
 27. The antenna defined in claim 23 wherein the temperaturemonitoring subsystem is operable to measure capacitance of a capacitorby matching conductive surfaces on the patch and iris layers in theaperture with liquid crystal therebetween, measuring capacitance of thecapacitor with a circuit coupled to the conductive surfaces, andcorrelating the capacitance to temperature of the liquid crystal. 28.The antenna defined in claim 22 wherein the heating elements are part ofa heater wire pattern on a superstrate between the patch substrate and abottom of the superstrate.
 29. The apparatus defined in claim 22 whereinthe array of RF antenna elements comprises a tunable slotted array ofantenna elements.
 30. The apparatus defined in claim 29 wherein thetunable slotted array comprises: a plurality of slots; a plurality ofpatches, wherein each of the patches is co-located over and separatedfrom a slot in the plurality of slots, forming a patch/slot pair, eachpatch/slot pair being turned off or on based on application of a voltageto the patch in the pair; and a controller to apply a control pattern tocontrol which patch/slot pairs are on and off to cause generation of abeam.
 31. A method comprising: monitoring a voltage across a currentsense resistor that is coupled in series with a transistor integratedonto a layer in the antenna and in contract with the liquid crystal;measuring the current through the current sense resistor; andcorrelating the current to the transistor temperature, the temperatureof the transistor being indicative of the liquid crystal temperature.32. The method defined in claim 31 wherein the layer is a patch layerhaving a plurality of patches, wherein each of the patches is co-locatedover and separated from a slot in a plurality of slots, forming apatch/slot pair.